A known pulse AC method ionizer that alternately generates positive ions and negative ions from a discharge electrode common to a positive side and a negative side to remove charges from a charge body is described in, for example, Patent literature (PTL) 1. This known ionizer has a high-voltage generating circuit as illustrated in FIG. 3. This high-voltage generating circuit has a positive-side transformer 32a, the primary side of which is connected to an alternating current power supply 30a by a switch 31a, and a negative-side transformer 32b, the primary side of which is connected to an alternating current power supply 30b by a switch 31b, the positive-side transformer 32a and negative-side transformer 32b being alternately connected to the alternating current power supply 30a and alternating current power supply 30b, respectively. The high-voltage generating circuit also has a positive-side high-voltage output circuit 33a connected to the secondary side of the positive-side transformer 32a, a negative-side high-voltage output circuit 33b connected to the secondary side of the negative-side transformer 32b, and a discharge electrode 34 connected to the positive-side high-voltage output circuit 33a and negative-side high-voltage output circuit 33b so as to be common to them. The positive-side high-voltage output circuit 33a and negative-side high-voltage output circuit 33b are alternately connected to the alternating current power supply 30a and alternating current power supply 30b through the transformer 32a and transformer 32b, respectively, so that the positive-side high-voltage output circuit 33a and negative-side high-voltage output circuit 33b alternately generate a positive high voltage and a negative high voltage, respectively. The generated positive high voltage and negative high voltage are alternately output to the discharge electrode 34, alternatively generating positive and negative ions from the discharge electrode 34.
The positive-side high-voltage output circuit 33a and negative-side high-voltage output circuit 33b are each formed with a Cockcroft-Walton circuit that includes a plurality of capacitors C and a plurality of diodes D.
Similar high-voltage generating circuits are also disclosed in PTL 2.
In the above ionizer, an output terminal 35 in the negative-side high-voltage output circuit 33b and an input terminal 36 in the positive-side high-voltage output circuit 33a are mutually connected with a connection line 37 so that when the positive-side high-voltage output circuit 33a and negative-side high-voltage output circuit 33b are mutually connected, an output from the negative-side high-voltage output circuit 33b becomes a reference potential of the positive-side high-voltage output circuit 33a. In this case, a ground terminal 38 in the positive-side transformer 32a and the input terminal 36 are isolated from each other by being disconnected from each other. Since the ground terminal 38 and input terminal 36 are isolated from each other in this way, there is the merit that the withstand voltage of the positive-side transformer 32a can be reduced.
When the ground terminal 38 and input terminal 36 are isolated from each other, however, alternate currents I1 and I2 generated due to a secondary voltage of the positive-side transformer 32a flows into both the positive-side high-voltage output circuit 33a and the negative-side high-voltage output circuit 33b during boosting by the positive-side high-voltage output circuit 33a as illustrated in FIG. 3, so their flow paths are prolonged. This is problematic in that the efficiency of generating the positive high voltage is lowered and the positive high voltage applied to the discharge electrode 34 is thereby lowered.
The alternate current I1 is a current at a time when the voltage on the secondary side of the transformer 32a is applied upward in the drawing. The alternate current I2 is a current at a time when the voltage on the secondary side of the transformer 32a is applied downward in the drawing.
The Cockcroft-Walton circuit is a circuit in which rectification by the diodes D and smoothing by the capacitors C are combined together to output a boosted direct-current high voltage. Since, in this circuit, the capacitors C repeat charging and discharging during smoothing, an alternating current component is superimposed on a direct-current high voltage Vo output from the high-voltage output circuits 33a and 33b, so the direct-current high voltage Vo has a ripple waveform as illustrated in FIG. 4. The ripple voltage is indicated by Vp. The symbol Vt in the drawing indicates the secondary voltage of the transformers 32a and 32b. 
During operation of the negative-side high-voltage output circuit 33b, therefore, when a negative high voltage entered from the output terminal 35 of the negative-side high-voltage output circuit 33b to the input terminal 36 of the positive-side high-voltage output circuit 33a passes through the positive-side high-voltage output circuit 33a, the ripple voltage Vp is boosted by the positive-side high-voltage output circuit 33a. As a result, another voltage arises that a negative high voltage output to the discharge electrode 34 is lowered. The negative high voltage is lowered at each connection stage in the Cockcroft-Walton circuit.